The present invention is generally related to measurements of optical tissues. In exemplary embodiments, the invention provides devices, systems, and methods for measuring optical errors of eyes, particularly for determining higher order refractive aberrations of the optical tissues of the eyes and/or other optical structures.
Known laser eye surgery procedures generally employ an ultraviolet or infrared laser to remove a microscopic layer of stromal tissue from the cornea of the eye. The laser typically removes a selected shape of the corneal tissue, often to correct refractive errors of the eye. Ultraviolet laser ablation results in photodecomposition of the corneal tissue, but generally does not cause significant thermal damage to adjacent and underlying tissues of the eye. The irradiated molecules are broken into smaller volatile fragments photochemically, directly breaking the intermolecular bonds.
Laser ablation procedures can remove the targeted stroma of the cornea to change the cornea's contour for varying purposes, such as for correcting myopia, hyperopia, astigmatism, and the like. Control over the distribution of ablation energy across the cornea may be provided by a variety of systems and methods, including the use of ablatable masks, fixed and moveable apertures, controlled scanning systems, eye movement tracking mechanisms, and the like. In known systems, the laser beam often comprises a series of discrete pulses of laser light energy, with the total shape and amount of tissue removed being determined by the shape, size, location, and/or number of laser energy pulses impinging on the cornea. A variety of algorithms may be used to calculate the pattern of laser pulses used to reshape the cornea so as to correct a refractive error of the eye. Known systems also make use of a variety of forms of lasers and/or laser energy to effect the correction, including infrared lasers, ultraviolet lasers, femtosecond lasers, wavelength multiplied solid-state lasers, and the like. Alternative vision correction techniques make use of radial incisions in the cornea, intraocular lenses, removable corneal support structures, and the like.
Known corneal correction treatment methods have generally been successful in correcting standard vision errors, such as myopia, hyperopia, and astigmatism. However, as with all successes, still further improvements would be desirable. Toward that end, wavefront measurement systems are now available to measure the refractive characteristics of a particular patient's eye. By customizing an ablation pattern based on wavefront measurements and providing improved laser system calibration, it may be possible to correct minor refractive errors so as to reliably and repeatably provide visual accuities greater than 20/20.
Known wavefront measurement methods often involve a somewhat time-consuming process to perform high precision measurements of the total aberrations of a patient's eye. So as to provide high-precision measurements of the irregular or high-order aberrations of the eye, the standard or sphero-cylindrical error may be largely corrected within the wavefront system. Existing wavefront techniques generally seek to limit the sphero-cylindrical error of the measured wavefront to about a diopter or less by compensating for standard errors of the eye using refractive correction optics. When correcting the standard refractive error of the eye within a wavefront system, many systems search for the best focus of the wavefront array pattern spot images formed by the lenslet array of the wavefront sensor. Although such techniques can be quite effective, the delays in taking individual wavefront measurements can be inconvenient, and may limit the accuracy of the overall wavefront measurement, and hence the effectiveness of treatment prescriptions which are derived from those wavefront measurements.
In light of the above, it would be desirable to provide improved optical measurement devices, systems, and methods. It would be particularly beneficial if these improved techniques could build on the recent advances that have been made in wavefront measurement techniques, particularly if improvements in efficiency and/or accuracy of the measurements could be provided. Systems and methods which could avoid or obviate the need for time consuming iterative searches for the best focus of spot images within a lenslet array spot pattern would also be desirable, particularly if such advantages could be provided without the complexity or cost of a full auto-refractor integrated with the wavefront measurements optics, without having to resort to manual entry of standard optical corrections based on phoropter measurements, or the like.